<?php
// Define a function to greet the user
function greetUser($name) {
    return "Hello, " . htmlspecialchars($name) . "!";
}

// Define a function to calculate the sum of two numbers
function calculateSum($a, $b) {
    return $a + $b;
}

// Define a function to check if a number is even
function isEven($number) {
    return $number % 2 === 0;
}

// Example usage
echo greetUser("John"); // Output: Hello, John!
echo calculateSum(5, 10); // Output: 15
echo isEven(4) ? "Even" : "Odd"; // Output: Even
?>